问题

使用 HTTP Client 请求 HTTPS 的 API 时出现 The certificate cannot be verified up to a trusted certification authority 异常，并且证书已经传入。

下面就是问题代码：

public class Program
{
    public static void Main(string[] args)
    {
        var url = @"https://xxx.xxx.xxx.xxx:xxxx/xxx-web/services/xxxx?wsdl";

        var handler = new HttpClientHandler
        {
            ClientCertificateOptions = ClientCertificateOption.Manual,
            ClientCertificates =
            {
                new X509Certificate2(@"E:\cert\rootTrust.cer","11111111"),
                new X509Certificate2(@"E:\cert\middleTrust.cer","11111111"),
                new X509Certificate2(@"E:\cert\wskey.pfx","ws654321")
            }
        };
        
        var webRequest = new HttpClient(handler);
        var result = webRequest.GetStringAsync(url).GetAwaiter().GetResult();
        Console.WriteLine(result);
    }
}

原因

因为在发出 HTTPS 请求的时候，HttpClient 都会检查 SSL 证书是否合法。如果不合法的话，就会导致抛出异常信息，而对方给出的证书是自签发的测试接口的证书，所以不是一个合法的 SSL 证书。

解决

在 HttpClientHandler 当中会有一个 ServerCertificateCustomValidationCallback 事件，该事件用于判定证书验证是否通过。我们可以挂接该事件，然后逻辑编写为直接返回 true 结果，这样就会忽略掉证书异常的情况。

最新的代码如下：

public class Program
{
    public static void Main(string[] args)
    {
        var url = @"https://xxx.xxx.xxx.xxx:xxxx/xxx-web/services/xxxx?wsdl";

        var handler = new HttpClientHandler
        {
            ServerCertificateCustomValidationCallback = (message, certificate2, arg3, arg4) => true, 
            ClientCertificateOptions = ClientCertificateOption.Manual,
            ClientCertificates =
            {
                new X509Certificate2(@"E:\cert\rootTrust.cer","11111111"),
                new X509Certificate2(@"E:\cert\middleTrust.cer","11111111"),
                new X509Certificate2(@"E:\cert\wskey.pfx","ws654321")
            }
        };
        
        var webRequest = new HttpClient(handler);
        var result = webRequest.GetStringAsync(url).GetAwaiter().GetResult();
        Console.WriteLine("xx");
    }
}